What to do if rocket is overstable?

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Why do people want to avoid weather cocking? Wouldn't the wind tend to bring the rocket back to the launch site during recovery as opposed to having it drift farther down range if the rocket had gone straight up? (Sorry if this is a dumb question, but I'm pretty new and just trying to understand things.)
 
Well, for me, it was kind of severe, and I lost about 900 feet of altitude. I don't know if it is related, but I had the mains set to deploy at 300', and they didn't come out until closer to 100'. So there wasn't much time to slow the descent.
 
I did not like the original RW one piece nosecone that came with my $99 Black Friday X-Celerator .... I purchased a FG nosecone like you did so I could be get the Nosecone with seperate shoulder to house my Garmin tracker. I have the same over stable config and fly on Aerotech K540M... just under 4,000ft, no weather cocking.... several flights.

Xcelerator launch crop.jpg

XCelerator.jpg
 
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Why do people want to avoid weather cocking? Wouldn't the wind tend to bring the rocket back to the launch site during recovery as opposed to having it drift farther down range if the rocket had gone straight up? (Sorry if this is a dumb question, but I'm pretty new and just trying to understand things.)

There are several reasons but one of the best ones to either avoid weather cocking or to properly account for it is the speed at deployment. If your rocket goes more in a cruise missle-ish trajectory with severe weather cocking it will deploy the chute at a pretty high velocity thus possibly damaging the airframe. The closer the rocket is to 0mph the closer it is to no airframe damage . Another reason is if motor ejection is used the delay time will likely be too long and tough to predict.
 
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Why do people want to avoid weather cocking? Wouldn't the wind tend to bring the rocket back to the launch site during recovery as opposed to having it drift farther down range if the rocket had gone straight up? (Sorry if this is a dumb question, but I'm pretty new and just trying to understand things.)

Not a dumb question. A small amount of weather cocking can do exactly what you said --- the rocket flies into the wind on ascent and then dfrifts back on the wind during descent. The problems are as described above --- the deployment can happen at high speed, and if using a set delay time, it can be too late.
 
You can fly the new two piece nose cone as an av bay and fly in 'short configuration ' without the lower coupler and upper airframe tube.

Put in the longer rail and use a motor that thurst curve says its off the pad at 60fps as suggested..if there is a hint of weather cocking you can fly short next time

Kenny
 
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Why do people want to avoid weather cocking? Wouldn't the wind tend to bring the rocket back to the launch site during recovery as opposed to having it drift farther down range if the rocket had gone straight up? (Sorry if this is a dumb question, but I'm pretty new and just trying to understand things.)

I've seen SEVERE weathercocking. It's not pretty and can be dangerous. When I was fairly newly into model rocketry, a schoolmate flew a Cineroc in wind that was too strong. It weathercocked badly and we saw the second stage kick off with it flying just about 30 degrees from horizontal. The rocket was lost. BTW, if you found a Cineroc near the University of Waterloo in 1979, I may know who flew it. Somewhere, I have the last known photo of it as it left the pad.
 
Seriously? 4000 ft. is hardly HPR territory.

Heck, some of us don't even have 4000 feet. One club's summer field is limited to about 3000 feet... The other club(with a waiver of 9000 to 12000) lost their field last year... :-(

Eldred
 
Since someone dredged up this thread, I'm happy to report that I have been able to fly this rocket on the J1520 VMAX to about 3000 with absolutely no weathercocking. I intend to try the J760 at the next launch. My problem was definitely not having enough speed off the pad.
 
Wind at altitude must be considered an have much impact on weather cocking regardless of stability.
 
Wind at altitude must be considered an have much impact on weather cocking regardless of stability.

I don't think winds at altitude are that much of an issue. You can watch a rocket that launches straight up and the smoke trail indicates that it is starting to move with the air mass. The rocket is still going straight up relative to the air, but relative to the ground it is starting to move with the wind. What that means is that when it gets to altitude, there is very little relative wind when measured from the rocket since it is moving with the moving air mass. In other word, the angle of attach on the fins is very small. Because of this, there would be very little wind on the rocket that could cause any weather cocking.
 
The problem I have with weathercocking is that it's neither controllable not predictable. You can figure if a rocket has a tendancy to weathercock, but until you hit the button you won't know by how much it's going to happen.
 
The problem I have with weathercocking is that it's neither controllable not predictable. You can figure if a rocket has a tendancy to weathercock, but until you hit the button you won't know by how much it's going to happen.

It is predictable, it's a function of the longitudinal moment of inertia, the CG/CP relationship, and the normal aerodynamic force. Those factors can be calculated and simulated fairly accurately by software such as openrocket.

If this is a matter of concern, you can use openrocket to determine the amount of weathercocking for a given level of wind for your rocket/motor combination. Graph this data onto a sheet using the wind speed as your x axis and the launch angle after weathercocking as your y axis, then take that sheet with you. You can then use the graph to predict the amount of weathercocking before launch.
 
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And it's controllable. If you angle your rail a few degrees downwind, your rocket will turn into the wind and end up going vertical since the apparent wind approaches zero angle of attack as the airspeed increases. That's also how iceboats work. Or launch the rocket on a vmax with a t/w >> 20. That virtually guarantees a vertical up flight.....

The negative aspect of this approach is that you will then experience the full wind drift, which can be as much as 2000' sideways for every 1000' of apogee. In those situations the right decision is not to launch.....but some folk simply don't have the maturity to make that decision.

Bob
 
Seriously? 4000 ft. is hardly HPR territory. .

I may be wrong. It could happen. I mean everyone CAN be wrong, right? But I digress. Last time I checked, HPR wasn't defined by altitude. It was defined by impulse and designation. If he wants to shove an M in a rocket and launch it to 1200 ft, so be it. So long as the flight is safe, sane and stable.

Our summer club only has 3000'. So it is that life goes on till the leaves fall and harvest is past.
 
"Young MC" rapper voice:

A girl starts walking guys start gawking
Sits down next to you and starts talking
Says she wants to dance cause she likes to groove
You're on a mission and your wishin'
Someone could cure your overstable condition

So come on fatso and just bust a fin
 
There's your problem. Unless the J360 has some bizzare curve. No need to look farther.

Why did you dredge up a 2.5-year-old thread? I solved the problem and don't even have this rocket any more. :confused2:
 
Since someone dredged up this thread, I'm happy to report that I have been able to fly this rocket on the J1520 VMAX to about 3000 with absolutely no weathercocking. I intend to try the J760 at the next launch. My problem was definitely not having enough speed off the pad.

John, I'm prepping a rocket for my L2 right now. Similar concern taking note of margin of 3, but weights are about the same as your rocket. I dismissed using anything in the 300 range early, just not enough trust. Even 400s might be marginal on a windy day. Very good chance I will use a J1055 vmax as the J760 just takes it to high for a shakedown flight. Want to see what's going on.
 
Why did you dredge up a 2.5-year-old thread? I solved the problem and don't even have this rocket any more. :confused2:

Funny me I thought forums where for the benefit of the entire community it serves, NOT just for the person who made the original post. :facepalm:
 
Funny me I thought forums where for the benefit of the entire community it serves, NOT just for the person who made the original post. :facepalm:

I stand corrected. However, you were solving a problem that was already solved earlier in the thread, so maybe there was no benefit to the entire community. :wink:
 
I stand corrected. However, you were solving a problem that was already solved earlier in the thread, so maybe there was no benefit to the entire community. :wink:

But what you don't realize is that you solved it for me too! And I'm confident you solved it for others that never posted. Look at my second post on this thread where I explain my plans for my L2. I have been considering using the vmax. Your real world experience corroborates my simulations and convinced me to a use the vmax unless winds are calm. This thread maybe directly responsible for a successful L2 attempt. :)
 
John, I'm prepping a rocket for my L2 right now. Similar concern taking note of margin of 3, but weights are about the same as your rocket. I dismissed using anything in the 300 range early, just not enough trust. Even 400s might be marginal on a windy day. Very good chance I will use a J1055 vmax as the J760 just takes it to high for a shakedown flight. Want to see what's going on.

This sounds like you're using the average thrust that is part of the motor designation
to make a determination of thrust to weight off the pad...
This is a very unsafe practice...
Motor thrust curves are not flat..
Always check the thrust curve,, it's the first quarter second or half second that counts...
This is why long burns usually have a spike in the thrust curve as soon as they ignite...

Teddy
 
This sounds like you're using the average thrust that is part of the motor designation
to make a determination of thrust to weight off the pad...
This is a very unsafe practice...
Motor thrust curves are not flat..
Always check the thrust curve,, it's the first quarter second or half second that counts...
This is why long burns usually have a spike in the thrust curve as soon as they ignite...

Teddy

Nope, not doing that at all Teddy...

Launch guide length: 71.9992 In.
Velocity at launch guide departure: 80.8015 ft/s
The launch guide was cleared at : 0.161 Seconds
User specified minimum velocity for stable flight: 45.0000 ft/s
Minimum velocity for stable flight reached at: 23.8709 In.

...but actually the vmax is pretty flat. :wink:

https://www.thrustcurve.org/simfilesearch.jsp?id=1303
 
Nope, not doing that at all Teddy...

Launch guide length: 71.9992 In.
Velocity at launch guide departure: 80.8015 ft/s
The launch guide was cleared at : 0.161 Seconds
User specified minimum velocity for stable flight: 45.0000 ft/s
Minimum velocity for stable flight reached at: 23.8709 In.

...but actually the vmax is pretty flat. :wink:

https://www.thrustcurve.org/simfilesearch.jsp?id=1303

Good man..
Look at the details of what is happening..
When I RSO I always ask "what's the thrust to weight off the pad"..
That's the single most important item..

Teddy
 
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